The present invention generally relates to two-speed transfer cases which use a planetary gear reduction set with a carrier that is surrounded by a variable controlled band brake assembly.
Most four-wheel drive vehicles utilize a transfer case of some sort that receives input torque from a transmission. The transfer case always provides output to a primary driveline, but its main purpose is to selectively provide output to a secondary driveline, and does so when the vehicle operator commands it. Typical transfer cases have various ways of engaging the secondary driveline, such as an operator actuated hydraulic clutch, or an automatic system that controls the clutch and works in response to various driving conditions, such as wheel slip.
Current transfer case designs utilize a planetary gear speed reduction assembly combined with a dog clutch or similar apparatus, to provide both a reduced speed drive through the use of the planetary gear assembly or a direct drive by directly coupling the input and output shafts of the transfer case together.
Several current methods that are used to shift the vehicle into and out of four-wheel drive demonstrate that the incorporation of the use of a transfer case into the complete operation of the vehicle has not been without its difficulties. In applications where a four wheel drive vehicle must be stopped and the automatic transmission placed in neutral to perform a range shift from high to low or vice versa. When this occurs the issue becomes trying to shift the transfer case against neutral drag torque of the automatic transmission. Thus the one obstacle in performing shifts within a transfer case is the synchronization of the high and low speed drives to the transmission output shaft.